1. Field of the Invention
The present invention relates to a jet-propulsion watercraft including a personal watercraft (PWC) which ejects water rearward and planes on a water surface as the resulting reaction, and more particularly to a cooling water passage structure of the jet-propulsion watercraft.
2. Description of the Related Art
In recent years, so-called jet-propulsion personal watercraft have been widely used in leisure, sport, rescue activities, and the like. The personal watercraft is configured to have a water jet pump that pressurizes and accelerates water sucked from a water intake generally provided on a hull bottom surface and ejects it rearward from an outlet port. Thereby, the personal watercraft is propelled.
In the jet-propulsion personal watercraft, a steering nozzle provided behind the outlet port of the water jet pump is swung either to the right or to the left, to change the ejection direction of the water to the right or to the left, thereby turning the watercraft to the right or to the left.
In the personal watercraft, part of the water pressurized by the water jet pump is supplied as cooling water to a water jacket of the engine and components requiring cooling. That is, a so-called xe2x80x9cdirect cooling systemxe2x80x9d in which water outside the watercraft is directly supplied to the components requiring cooling, is employed.
The xe2x80x9cdirect cooling systemxe2x80x9d advantageously offers high cooling performance with a simple structure. In this system, however, unwanted substances are taken into the cooling water passage, together with the cooling water, because the water outside the watercraft is directly supplied to the cooling water passage. When the cooling water passage is clogged with the substances, its cooling capability is degraded. Especially when the cooling water passage to the exhaust passage connected to the engine is occluded by the substances, the cooling water is not supplied to an exhaust gas flowing through the inside of the exhaust passage through a xe2x80x9cwater-supply holexe2x80x9d provided in the exhaust passage, which leads to an increase in the temperature of the exhaust gas. Besides, rubber connecting components provided in the connected portion of the exhaust passage would be deteriorated.
Conventionally, for the purpose of detecting trouble in the cooling water passage, the cooling water passage is provided with a water-temperature sensor or the like.
The present invention addresses the above-described condition, and an object of the present invention is to provide a jet-propulsion watercraft capable of maintaining a cooling capability in an exhaust passage even when one cooling water passage to the exhaust passage is clogged with substances. Another object of the present invention is to provide a jet-propulsion watercraft having a cooling water passage structure capable of quickly eliminating substances in a cooling water passage formed in an exhaust passage.
According to the present invention, there is provided a jet-propulsion watercraft comprising: an engine having a cooling water passage inside thereof; an exhaust passage extending from the engine and having a double-walled structure comprised of inner and outer walls between which a cooling water passage is at least partially formed, for discharging an exhaust gas; a water jet pump driven by the engine, the water jet pump pressurizing and accelerating water taken in from outside of the watercraft and ejecting the water from an outlet port to propel the watercraft as a reaction of the ejecting water, and supplying part of the water to the cooling water passage of the engine and the cooling water passage of the exhaust passage; a water-supply hole formed in the inner wall of the double-walled structure, for supplying the water into an exhaust gas passage in the exhaust passage; a first cooling water passage for supplying the cooling water to the cooling water passage between the outer wall and the inner wall of the double-walled structure; and a bypass passage formed independently of the first cooling water passage, for supplying the cooling water to the cooling water passage between the outer wall and the inner wall.
In the jet-propulsion watercraft so constituted, when either the first cooling water passage or the bypass passage is clogged with substances, the cooling capability of the exhaust passage can be maintained because the cooling water is supplied to the exhaust passage through the remaining one. As a result, regardless of clogging in the first cooling water passage or the bypass passage, the temperature and noise of the exhaust gas can be reduced. Therefore, a rubber connecting component used in a connected portion of the exhaust passage is not deteriorated.
In the jet-propulsion watercraft, the bypass passage may be connected to the cooling water passage between the outer wall and the inner wall of the double-walled structure through a connecting hole provided in the outer wall, and the water-supply hole through which the water is supplied into the exhaust gas passage may be formed in the inner wall which can be reached by a drill through the connecting hole such that a diameter of the water-supply hole is smaller than a diameter of the connecting hole. Thereby, even when the water-supply hole is clogged with substances, such substances can be easily eliminated through the connecting hole. Besides, the water-supply hole can be easily formed by utilizing the connecting hole.
In the jet-propulsion watercraft, the water-supply hole may be concentric with the connecting hole. Thereby, by using one drill with a small-diameter drill protruding from a large-diameter drill, i.e., a core drill with center drill, two holes can be simultaneously formed by one drilling operation. This improves productivity.
In the jet-propulsion watercraft, the connecting hole may be a taper hole, a female screw may be provided on an inner peripheral face of the taper hole, and a male screw may be provided at a tip end of a pipe constituting the bypass passage so as to be threadedly engaged with the female screw. This achieves tight liquid sealing in the connecting structure.
In the jet-propulsion watercraft, a tip end portion of the bypass passage may be bent to be L-shaped and a tip end of the L-shaped tip end portion may be connected to the connecting hole, and a penetrating hole may be formed to extend from a first face of the tip end of the L-shaped tip end portion to a second face of a bent portion of the L-shaped tip end portion, the second face being opposed to the first face, and a cap member may be removably screwed to the penetrating hole opened in the second face. Thereby, the mere removal of the cap member from the penetrating hole enables the water-supply hole to be inspected and the substances clogging the water-supply hole to be eliminated. Preferably, the cap member is provided with a transparent inspection port.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.